Begin lying on your back with legs bent
*Beginners — start with only the legs. If you do not feel it in your back you can add your arms. Stronger muscles like the back extensors can take over in this exercise. Starting with the legs only should prevent that.
Lift your legs and arms off the ground, keeping your knees bent. Lower one arm to the ground and lower your opposite leg at the same time. Repeat with your opposite arm and leg. Continue to alternate. Maintain your low back on the floor and keep abdominals drawn down towards your spine. If you cannot maintain lower back, start by alternating arms. As you become stronger alternate legs only. Then progress to opposite arm and leg.